This invention relates generally to the field of hard disc drive data storage devices, and more particularly, but not by way of limitation, to a new system for mounting the discs to the hub of a spindle motor in a disc drive.
Disc drives of the type known as xe2x80x9cWinchesterxe2x80x9d disc drives, or hard disc drives, are well known in the industry. Such disc drives magnetically record digital data on a plurality of circular, concentric data tracks on the surfaces of one or more rigid discs. The discs are typically mounted for rotation on the hub of a brushless DC spindle motor. In disc drives of the current generation, the spindle motor rotates the discs at speeds of up to 15,000 RPM.
Data are recorded to and retrieved from the discs by an array of vertically aligned read/write head assemblies, or heads, which are controllably moved from track to track by an actuator assembly. The read/write head assemblies typically consist of an electromagnetic transducer carried on an air bearing slider. This slider acts in a cooperative aerodynamic relationship with a thin layer of air dragged along by the spinning discs to fly the head assembly in a closely spaced relationship to the disc surface. In order to maintain the proper flying relationship between the head assemblies and the discs, the head assemblies are attached to and supported by head suspensions or flexures.
The actuator assembly used to move the heads from track to track has assumed many forms historically, with most disc drives of the current generation incorporating an actuator of the type referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing base member closely adjacent the outer diameter of the discs. The pivot shaft is mounted such that its central axis is normal to the plane of rotation of the discs. An actuator bearing housing is mounted to the pivot shaft by an arrangement of precision ball bearing assemblies, and supports a flat coil which is suspended in the magnetic field of an array of permanent magnets, which are fixedly mounted to the disc drive housing base member. On the side of the actuator bearing housing opposite to the coil, the actuator bearing housing also typically includes a plurality of vertically aligned, radially extending actuator head mounting arms, to which the head suspensions mentioned above are mounted. When controlled DC current is applied to the coil, a magnetic field is formed surrounding the coil which interacts with the magnetic field of the permanent magnets to rotate the actuator bearing housing, with the attached head suspensions and head assemblies. As the actuator bearing housing rotates, the heads are moved radially across the data tracks along an arcuate path.
Disc drives of the current generation are included in desk-top computer systems for office and home environments, as well as in laptop computers which, because of their portability, can be used wherever they can be transported. Because of this wide range of operating environments, the computer systems, as well as the disc drives incorporated in them, must be capable of reliable operation over a wide range of ambient temperatures.
Furthermore, laptop computers in particular can be expected to be subjected to large amounts of mechanical shock as they are moved about. It is common in the industry, therefore, that disc drives be specified to operate over ambient temperature ranges of from, for instance, xe2x88x925 degrees Celsius to 60 degrees Celsius, and further be specified to be capable of withstanding operating mechanical shocks of 100 G or greater without becoming inoperable.
One of the areas of disc drive design which is of particular concern when considering ambient temperature variations and mechanical shock resistance is the system used to mount and clamp the discs to the spindle motor. During manufacture, the discs are mounted and clamped to the spindle motor in a temperature- and cleanliness-controlled environment. Once mechanical assembly of the disc drive is completed, special servo-writers are used to prerecord servo information on the discs. This servo information is used during operation of the disc drive to control the positioning of the actuator used to move the read/write heads to the desired data location in a manner well known in the industry. Once the servo information has been recorded on the discs, it is assumed by the servo logic that the servo information, and all data subsequently recorded, are on circular tracks that are concentric with relation to the spin axis of the spindle motor. The discs, therefore, must be mounted and clamped to the spindle motor in a manner that prevents shifting of the discs relative to the spindle motor due to differential thermal expansion of the discs and motor components over the specified temperature range, or due to mechanical shock applied to the host computer system.
Several systems for clamping of the discs to the spindle motor exist. In each of these disc clamping systems, the spindle motor of the disc drive includes a disc mounting flange extending radially from the lower end of the spindle motor hub. A first disc is placed over the hub during assembly and brought to rest on this disc mounting flange. An arrangement of disc spacers and additional discs are then alternately placed over the spindle motor hub until an intended disc stack is formed. Finally, some type of disc clamp is attached to the spindle motor hub which exerts an axial clamping force against the uppermost disc in the disc stack. This axial clamping force is passed through the discs and disc spacers and squeezes the disc stack between the disc clamp and the disc mounting flange on the spindle motor hub.
It is important that the discs and clamp are centered on the hub so to insure that the discs are balanced when rotating at high speeds. Imbalances are partially caused by the tolerances between the spindle and the clamp inner diameter. Because the clamp has to slide onto the spindle, there is room for the clamp to move relative to the spindle. For example, typically a clamp inner diameter has a tolerance of xc2x10.002 inches. These tolerance limitations cause imbalances when the disc is rotating due to movement between the spindle and the clamp. A method used to correct imbalances caused by limitations of the existing systems is to bias the discs on the hub.
An example of a disc pack assembly of the prior art is shown in FIG. 1. As is generally known in the art, the illustrative disc drive unit 610 includes a head positioner assembly 611 mounted within the housing 616 at a position along the disc pack. A central shaft 620 having a central axis is securely fixed to a portion of the housing 616, and information storage disks 614 are mounted for rotational movement within the housing 616 about the shaft 620. A first information storage disc 614 is stacked on top of a hub flange 632. A disc spacer 648 is stacked on top of the first information disc and a second disc 614 is stacked on top of the disc spacer 648. A disc clamp assembly 658 including a clamp ring 660 and a grip ring 662 secure the information storage discs to the spindle hub 626. The clamping ring 660 has an inner diameter larger than the outer diameter of the spindle hub 626, so that the clamping ring 660 can be slipped over the spindle hub 626 and rest on the top surface of the support ring 649. Generally, the clamping ring 660 further has a rounded convex surface 664 near the outer periphery, so that the clamp force is applied away from the inner diameter of the information storage discs 614. The clamping ring further has a raised inner portion 666 on which the lower surface of the grip ring 662 rests.
There is a need for a simple means and device to align the clamping assembly components in a disc drive during assembly such that they are and accurately centered on the disc pack. The present invention, described below, provides a solution to this and other problems, and offers other advantages over the prior art.
Against this backdrop the present invention has been developed. An embodiment of the present invention is directed to a disc clamp tolerance ring for reducing movement of the disc clamp, and allowing the disc clamp to be more precisely centered on the spindle. The disc clamp tolerance ring is located between an inner diameter of the disc clamp and the spindle. The disc clamp tolerance ring allows the disc clamp to be centered on the spindle and eliminates relative movement between the disc clamp and the spindle due to the tolerances in each part.
In another embodiment, a disc pack assembly includes a spindle motor hub rotatable and symmetrical about a central axis therethrough. The spindle hub includes a bottom hub flange extending radially outward therefrom and a clamp retainer portion axially extending from an upper end of the hub. The retainer portion further includes a cylindrical outer surface. The disc pack assembly further includes at least one information storage disc stacked on the spindle hub and resting on the bottom flange and an annular disc clamp securing the information storage disc to the spindle hub. The disc pack assembly further includes a disc tolerance ring located between the spindle hub and the disc clamp.
In another embodiment, a disc clamp assembly includes a disc clamp for securing an information storage disc on a spindle hub in a disc drive and means for compliantly centering the disc clamp on the spindle hub.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.